The most common sea shells found on modern beaches are mollusks (phyllum Mollusca). The most commonly observed mollusks types (classes) are clams (Pelecypoda), snails (Gastropoda), and squids and octopi (Cephalopoda). These classes also represent the most common mollusk fossils in Kentucky. Mollusk fossils representing all three of these classes are found in the Ordovician, Silurian, Devonian, Mississippian, and Pennsylvanian rocks of Kentucky.

Some of the mollusk fossils found in the Eastern Kentucky Coal Field still retain their mother-of-pearl luster and even color patterns.